1. Field of the Invention
The present invention relates to a mobile communication system and, more particularly, to an alarm method and apparatus for informing a base station that a repeating module is out of order in a mobile communication repeating system having a plurality of repeating modules.
2. Description of the Related Art
A cellular system, which is a typical mobile communication system, provides communication services for a plurality of mobile stations from base stations that are positioned at regular intervals. The base stations are situated at fixed locations, whereas the mobile station travels according to the position of a user. The mobile station may sometimes be located in radio wave shadow areas, such as in the interior of a building, subway station or arcade or in the closed space of an elevator. When a radio wave from the base station is transmitted to such an area, there is a great path loss. For instance, the radio wave at the interior of a building is characterized by multipath fading having a very short delay. Consequently, the signal performance diminishes when the radio wave is transmitted from the base station to the interior of a building. Moreover, if the radio wave is transmitted from the base station to the rear of a wall or an elevator, the signal performance diminishes due to a shadow phenomenon which makes it difficult to provide communication services to a mobile station located in such radio wave shadow areas as a result of the signal degradation.
Therefore, certain techniques have been proposed for enlarging a communication service area irrespective of the position of the mobile station. For example, the techniques disclosed in U.S. Pat. No. 5,280,472 to Gilhousen, et al., entitled "CDMA MICROCELLULAR TELEPHONE SYSTEM AND DISTRIBUTED ANTENNA SYSTEM THEREFOR", and Korean Patent Application No. 96-15231 filed by Chang-hyun Oh, on May 9, 1996, for repeating a code division multiple access (CDMA) communication signal (in a CDMA system) between a plurality of distributed antennas and base station transceivers and in a CDMA system having a plurality of "delay elements" or "distributed elements" which are repeating modules that communicate with the mobile station through each antenna. This distributed antenna system provides multipath signals for facilitating signal diversity. Consequently, the communication services can be supplied to mobile stations located in radio wave shadow areas, thereby improving the performance of the system.
In the above disclosed mobile communication systems, however, the repeating modules are remotely located from the base station and are operated by unmanned control. Therefore, the base station can not determine if any of the repeating modules are out of order. For example, each repeating module displays only a power ON/OFF state via a light emitting diode (LED) which is installed at its front surface. Indeed, these systems do not provide methods for either checking whether the repeating module is out of order, displaying a failure indication or informing the base station that the repeating module is out of order. Therefore, the base station cannot monitor an alarm state of the repeating module. Consequently, both the management efficiency and the reliability of the system is diminished and degraded.